This program project is a coordination of three areas. In the first, the efficacy of azithromycin for intervention and community-based control of trachoma in three sociologically different African countries will be determined. We will use DNA amplification and antigen detection for Chlamydia trachomatis from prospectively obtained ocular and nasopharyngeal samples over a four year period. Secondly, the epidemiology of re-emergent disease will be addressed by using nucleic acid sequencing of amplified chlamydial DNA from sequential samples. Thirdly, the immunology of re-emergent disease will be examined by measuring type specific antibodies in tears to linear peptides generated from the DNA sequencing data. The Microbiologic Core will determine baseline levels of chlamydial ocular and nasal infection for the entire study in Egypt and Tanzania by PCR-EIA and antigen EIA. We will interdigitate with Projects 1 and 2 on response of infection to treatment at 2, 3 and 4 months, and on the development of re-emergent disease at 6, 9, 12, 15, 18 and 24 months. In addition, the Microbiologic Core will produce the DNA to be used for sequencing and antibody studies by Project 3. Finally, the Microbiologic Core will standardize and monitor quality control of PCR and EIA assays to be used by all sites.